1. Technical Field
The invention relates to a radiological image detection apparatus used in a medical radiological imaging system, or the like and a method of manufacturing the same.
2. Related Art
DR (Digital Radiography) using a radiological image detection apparatus, like an FPD (Flat Panel Detector) that converts a radiological image, such as an X-ray image, into digital data, has recently been put into practice. When compared with a related art CR (Computed Radiography) system that uses an imaging plate made of a photostimulable phosphor (an accumulative phosphor), the radiological image detection apparatus has an advantage of being able to ascertain an image immediately. Thus, the DR has become proliferated rapidly.
Various types of radiological image detection apparatuses have already been put forward. One of the radiological image detection apparatuses is of a known indirect conversion type. This type of radiological image detection apparatus temporarily converts X-radiation into visible light by means of a scintillator, like a CsI: Tl scintillator and a GOS (Gd2O2S:Tb) scintillator, and a semiconductor layer converts the visible light into electric charges and accumulates the resultant electric charges (see; for instance, Patent Document 1 (JP-A-2011-17683)).
In the X-ray image detection apparatus described in connection with Patent Document 1, the scintillator is exposed to X-ray applied in the direction of the photodetecting unit. In such a configuration, a short distance exists between the principal light emission area on the X-ray entrance side of the scintillator and the photodetecting unit, so that a high resolution detected image can be acquired. In the meantime, a substrate of the photodetecting unit disposed on the X-ray entrance side of the scintillator unavoidably absorbs X-ray, which raises a problem of a decrease in the quantity of X-ray entering the scintillator.
The photodetecting unit is built by inclusion of a photodiode (PD) and a TFT (Thin Film Transistor) that each are formed from a-Si, or the like. Alkali-free glass is usually used for a substrate supporting the PD and the TFT. The reason for this is that, when soda glass is used, a-Si may be contaminated with Na that will stem from glass during formation of an a-Si film in the presence of high temperature, which may in turn deteriorate performance of an element. However, alkali-free glass is more expensive than soda glass and also absorbs a larger amount of X-ray than does the soda glass. For instance, when an X-ray shaped beam generated at a tube voltage of 50 kV is used by applying a filter having Al equivalent weight 2 mm to the photodetecting unit, an X-ray absorption factor exhibited by the alkali-free glass substrate comes to as high as 16.8%. Specifically, the light reaches the scintillator while 15% or more of X-ray with which the photodetecting unit has been irradiated is lost as a result of X-ray being absorbed by the substrate. As mentioned above, when consideration is given to maintaining the performance of the a-Si film, using alkali-free glass for the substrate is indispensable. As a result of X-ray being absorbed by the substrate, a great decline in the amount of X-ray entering the scintillator is unavoidable. Specifically, a high image quality feature that is yielded when the scintillator is exposed to X-ray emitted from the direction of the photodetecting unit is diminished.
Patent Document 2 (JP-A-2009-133837) and Patent Document 3 (JP-A-2008-235649) describe peeling and removal of the substrate after the photodetecting unit has been formed by forming a sensor on the substrate. Such a radiological image detection apparatus including the photodetecting unit that does not have the substrate can be said to be preferable as to absorption of radiation caused by the substrate.
However, in relation to the type of the radiological image detection apparatus that irradiates the scintillator with X-ray emitted from the direction of the photodetecting unit, if the substrate is peeled off from the photodetecting unit as described in connection with Patent Documents 2 and 3, new problems, such as those which will be mentioned below, may arise. Namely, damage will be inflicted on the photodetecting unit if the strength of the photodetecting unit cannot be maintained. The photodetecting unit will be corroded by moisture included in the outside air. Alternatively, performance of the scintillator will be deteriorated by moisture permeation by way of the thin photodetecting unit. A demand exists for solving these problems incidental to peeling of the substrate, to thus enhance image quality much greater.